DOJ's Holder says agency is investigating Target data breach

The U.S. Department of Justice is investigating the data breach at Target stores, which compromised as many as 110 million payment cards and personal records in one of the largest such attacks on record.

The U.S. Department of Justice is investigating the data breach at Target stores, which compromised as many as 110 million payment cards and personal records in one of the largest such attacks on record.

Attorney General Eric Holder told the U.S. Senate Judiciary Committee on Wednesday that "we are committed to working to find not only the perpetrators of these sorts of data breaches -- but also any individuals and groups who exploit that data via credit card fraud."

The DOJ veered from its normal protocol in revealing its probe. Holder said the DOJ generally does not discuss matters under investigation but did not say why it made an exception in this case. The U.S. Secret Service is also investigating, and other cyberdefense organizations in the U.S. government are contributing.

Michaels, an arts and crafts chain, said on Saturday it was alerting customers after possible unauthorized charges were discovered from cards used at its stores. The company said it is investigating whether a breach occurred.

The Target data breach has led computer security experts to study the economy around stolen card data. It is suspected that many more retailers may have been compromised, with attackers focusing on point-of-sale devices.

The malware used against Target was a "RAM scraper," which intercepted unencrypted payment card data on the POS device. It is unknown how intruders gained access to Target's network, but it appears they gained wide leverage, taking more than 11GB of data.